The formulation of a high performance sunscreen product requires many ingredients. Most important of which is the sunscreen active. Since sunscreens are considered by the Food and Drug Administration (FDA) as a drug, the actives that can be used are carefully regulated. Some of these materials do however experience photodegradation in formulation. It is the minimization of this type photodegradation issues that the present invention is directed.
Ultraviolet radiation from the sun or artificial sources can damage materials and/or coatings containing photoactive substances, such as photoactive polymers, pigments and dyes, by altering chemical bonds in the structure of the polymer, pigment, or dye. This photodegradation can lead to color fading, loss of gloss, and/or loss of physical and protective properties of a photodegradable or photoactive polymer or coating. Understandably, photostabilizing or photostabilization is the process or effect of preventing the photodegradation of photoactive substances. In particular, photostabilizing can be increasing the light fastness of a composition, preventing yellowing, or color formation, and delaying or preventing photochemical reactions that adversely affect photoactive substances.
One method to protect photoactive substances is through the use of UV filters; one class of materials particularly suited to act as a UV filters are naphthalate polyesters, for example those patented by this assignee. Naphthalate polyesters are suitable UV filters because they have very high extinction coefficients and subsequently low transmission of ultraviolet (UV) radiation. Additionally, the incorporation of naphthalates into polyester polymers increase the polymer's thermal and structural stability, decrease the polymer's gas permeability, and dramatically block the transmission of UV radiation through the polymer. The UV filtering and improved physical characteristics have led to the use of naphthalate polymers and blends in a wide range of applications including beverage and personal care product packaging, protective screening films, sail cloth fiber and as an additive stabilizer in sunscreens and cosmetics.
While efficiently absorbing UV radiation, naphthalates dissipate (emit) the absorbed energy through fluorescence. Fluorescence is a type of luminescence in which an atom or molecule emits radiation, i.e., a photon, in passing from a higher to a lower electron state, as described in my co-pending application Ser. No. 11/891,280 filed Aug. 9, 2007, herein incorporated by reference. The term is restricted to phenomena in which the time interval between absorption and emission energy is extremely short. This fluorescence can be a positive attribute in enabling the ready detection of naphthalate containing polymers or in the development of fluorescent coatings and inks. Alternatively, the high absorption of UV radiation can produce color formation or yellowing after exposure to UV light. Although this yellowing may not impact mechanical and physical properties of the polymer, it is generally undesirable. The fluorescence, color formation, or yellowing phenomena are of concern especially in packaging of products when the product's appearance is to be as close to its natural state as desired. For example, in the packaging of foods and beverages, if food or beverages were inside a poly(ethylene-2,6-naphthalene dicarboxylate) (“PEN”) container they may appear unnaturally colored.
Quenching fluorescence eliminates or reduces photon emission by providing an alternative pathway for the excited state energy, such as radiative loss (heat), or intersystem crossing to an excited triplet state. Methods to quench fluorescence in PEN have been disclosed, for example see references cited in U.S. Pat. No. 6,001,952. These examples disclose the use of o-chlorophenol to quench PEN fluorescence in chloroform solutions. Dissolving PEN in a chloroform solution to disperse a fluorescence quencher, however, is not practical since the PEN must have a low molecular weight to dissolve in the chloroform solution and only very dilute PEN solutions can be prepared.
Other compounds used to quench naphthalate fluorescence include: benzotriazoles, cyanoacrylates, benzophenones, and benzoxazinones (JP Pat. No. 08225672); cyclic imino esters or quinoxalines (EP Pat. No. 0711803); and benzylidene compounds (U.S. Pat. Nos. 4,617,374, 4,707,537, and 6,001,952). Many of these examples are disadvantageous because they require postproduction coating of fluorescent materials, show inadequate reduction in the fluorescence from fluorescent materials, or are only effective in very dilute solutions. Accordingly, there is a need for naphthalate compositions having a reduced fluorescence without deleteriously affecting the physical properties of the polymer.
The absorption of ultraviolet light by a chromophore-containing organic molecule causes the excitation of an electron in the chromophore moiety from an initially occupied, low energy orbital to a higher energy, previously unoccupied orbital. The energy of the absorbed photon is used to energize an electron and cause it to “jump” to a higher energy orbital, see Turro, Modern Molecular Photochemistry, 1991. Two excited electronic states derive from the electronic orbital configuration produced by UV light absorption. In one state, the electron spins are paired (antiparallel) and in the other state the electron spins are unpaired (parallel). The state with paired spins has no resultant spin magnetic moment, but the state with unpaired spins possesses a net spin magnetic moment. A state with paired spins remains a single state in the presence of a magnetic field, and is termed a singlet state. A state with unpaired spins interacts with a magnetic field and splits into three quantized states, and is termed a triplet state.
In the electronically excited state, the chromophore-containing organic molecule is prone to degrade via a number of known pathways and, therefore, can absorb little or no additional UV light. To photostabilize an electronically excited chromophore-containing organic molecule in order to provide sufficient UV protection, it must be returned to the ground state before it undergoes a photochemical reaction destructive to its UV absorbing capability. There are known photostabilizing sunscreen additives, such as Octocrylene, methylbenzilydene camphor, and the esters or polyesters of naphthalene dicarboxylic acid of this assignee's U.S. Pat. Nos. 6,113,931; 6,284,916; 6,518,451; and 6,551,605, all hereby incorporated by reference, that are capable of quenching excited triplet state energy. Alkoxy crylenes, particularly methoxy crylenes, return chromophore-containing organic molecules, particularly butyl methoxydibenzoylmethane (Avobenzone), octyl methoxycinnamate (Octinoxate), and octyl salicylate (Octisalate), from both an electronically excited singlet state and excited triplet state back to their ground state, thereby photostabilizing the UV-absorbing organic molecules.
A compound known to those skilled in the art is iscotrizinol. This material sold under the trade name Unasorb ET by 3V Sigma, has the following structure and identifiers.

The product has the following properties reported by 3V Sigma the manufacturer.